Molds are often used during processing of biological specimen e.g. for fixing such specimen in a block of an embedding material. For example, molds, typically made of stainless steel, are used for embedding samples of biopsy tissues in a paraffin block. Such embedding is carried out as a preliminary step before sectioning the samples for examining the tissues e.g. under a microscope in a histopathology laboratory.
Biopsy tissues may be obtained from a live organ using one of various methods. The following description relates to obtaining and processing core biopsy tissues for histopathology; however relevant steps of the method described below are commonly employed for preparation of other types of biopsy tissues as well.
Core biopsy is a routine procedure used to obtain a sample of a biological tissue using a core biopsy needle. The obtained sample tissue has a typical shape of a long and narrow stripe—e.g. about 20 mm long and about 1 mm wide. A typical preparation process of a core biopsy sample prior to examination is detailed for example in U.S. Pat. No. 7,156,814, and may include the following steps:
a. The biological sample is placed in a sample box, possibly after being submerged in a preservative solution. Inside the sample box the sample is gently pressed, using a box cover, between two sheets of a soft material such as a sponge, which prevents displacement of the sample tissue inside the box. An example of a sample box is Tissue-Tek® Uni-Cassettes® by SAKURA FINETEK USA, INC. The sample box is then marked with an alpha-numeric string (e.g. digits and letters) identifying the sample and its origin.
b. The tissue inside the box may be taken through a chemical process, possibly of several hours, intended to fixate and dry the sample. The chemical process may include immersion in neutral buffered formaldehyde preservative solution, in ethanol, in xylene and/or in paraffin. Then the sample tissue is dried.
c. Dried tissue is removed from the sample box and placed in a mold, the mold being about the size of the sample box. The sample tissue is fixed to the compartment floor of the mold, typically using a drop of liquid paraffin and by gently pressing onto the sample tissue until the paraffin solidifies. An example of a metal mold is Tissue-Tek® Compartment floor Molds by SAKURA FINETEK USA, INC.
d. The sample box, without cover, is fixed on top of the metal mold, and the space within, that is to say between the metal mold and the sample box, is filled with liquid paraffin.
e. After the block of paraffin solidifies the metal mold is removed, leaving the sample box (with the marked string identifying the sample tissue) filled with a block of paraffin and with the sample tissue on top.
f. The sample box with the sample tissue is taken for slicing. Slices of typical thickness of a few microns are taken from the top surface of the paraffin block, carrying slices of the sample tissue therein.
g. Selected slices are placed between two glass plates and inserted to an oven for melting the paraffin. After removing the liquid paraffin, the sample tissue between two glass plates is taken for examination, e.g. under a microscope.
U.S. Pat. No. 5,612,218 discloses a mould for embedding a tissue sample in a paraffin block, having a recess with a bottom. Provided in the bottom of the recess is a cavity whose cross-section corresponds substantially to the cross-section of the tissue sample.
Some methods for processing sample tissues include, prior to embedding the sample tissue in a block, attaching the sample tissue to a sample sheet. Some such methods are described in international patent application publication WO 2013/105095, filed on Jan. 10, 2013, which is incorporated herein by reference in its entirety. Such a sample sheet may adhere to a biological tissue upon manually pressing on, or adjoining the biological tissue and the sample sheet. Such a sample sheet can further maintain adherence with the biological tissue, and the biological tissue remains stuck to the sample sheet following immersion in water solutions such as formaldehyde and during a chemical process applied to the sample tissue in preparation to examination, as described above. Examples for a sample sheet as described herein include: a mesh film of cellulose esters such as Immobilon-NC Transfer Membrane by Millipore™; a film such as Mixed Cellulose Esters Membrane ME 25 or WME by Whatman Ltd; and a film such as Supor® 200 PES Membrane Disc Filter by Pall Corporation or NL-17 or Super charged membrane by Whatman Ltd. Further examples for a sample sheet may include a film such as Cellulose Filters, for example grade 1 or grade 42 or grade 542, by Whatman Ltd. Further examples for a sample sheet may include a mesh film of cellulose esters covered with glue or another adhesive material so that sample tissues adhere to it. Examples for a sample sheet may further include paper, or another thin and flexible sheet that may adhere to a sample tissue upon contact the sample tissue and the sample sheet or upon adjoining the sample tissue and the sample sheet, by glue, adhesive forces, electrostatic forces or using any other technique.